linux-kernel - Re: [PATCH] HID: sony: Enable Gasia third-party PS3 controllers

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Message-ID: <alpine.LNX.2.00.1503162236420.25438@pobox.suse.cz>
Date:	Mon, 16 Mar 2015 22:37:18 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Pavel Machek <pavel@....cz>
cc:	Oliver Neukum <oneukum@...e.de>, Lauri Kasanen <cand@....com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	ao2@....it, AndrewD207@....com
Subject: Re: [PATCH] HID: sony: Enable Gasia third-party PS3 controllers

On Mon, 16 Mar 2015, Pavel Machek wrote:

> > > Oliver Neukum <oneukum@...e.de> wrote:
> > > 
> > > > > +	ret = usb_interrupt_msg(dev, usb_sndintpipe(dev, 0x02),
> > > > > +				buf2, sizeof(buf2),
> > > > > +				&transfered, USB_CTRL_SET_TIMEOUT);
> > > > 
> > > > You cannot do this. Even for a single byte DMA on the stack is
> > > > wrong. Not on all architectures it works at all and you violate
> > > > the DMA constrainsts. You must use kmalloc().
> > > 
> > > Hi Oliver,
> > > 
> > > Does this still apply when using hid_hw_output_report?
> > 
> > Yes. For USB devices hid_hw_output_report() goes to
> > usbhid_output_report(). That goes to usb_interrupt_msg(),
> > which passes the buffer pointer. It will then be mapped
> > for DMA. You must not do that on the stack.
> 
> Should we have some kind of runtime test for this ...? Because this is
> very very easy to get wrong... and I bet we do get it wrong at > 1
> place...

Are you sure CONFIG_DMA_API_DEBUG wouldn't warn here?

-- 
Jiri Kosina
SUSE Labs
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